Abstract
A rapidly growing body of literature in several organisms suggests that environmentally-induced adaptive changes in phenotype can be transmitted across multiple generations. Although within-generation plasticity has been well documented, multigenerational plasticity represents a significant departure from conventional evolutionary thought. Studies of C. elegans have been particularly influential because this species exhibits extensive phenotypic plasticity, it is often essentially isogenic, and it has well-documented molecular and cellular mechanisms through which nongenetic inheritance occurs. However, while experimentalists are eager to claim that nongenetic modes of inheritance characterized in this and other model systems enhance fitness, many biologists remain skeptical given the extraordinary nature of this claim. We establish three criteria to evaluate how compelling the evidence for adaptive multigenerational plasticity is, and we use these criteria to critically examine putative cases of it in C. elegans. We conclude by suggesting potentially fruitful avenues for future research.
Highlights
Biologists have long been interested in why organisms appear to be well-suited to the environments in which they find themselves
There have been two main explanations: Lamarckism organisms change over the course of their lifetimes in ways that make them more suited to their environment, and these beneficial attributes are transmitted to their offspring, or Darwinism organisms are largely fixed during their lifetimes, but those that are best suited to their environment survive and/or reproduce best, passing their attributes to their offspring
These two explanations are not mutually exclusive, but this dichotomy was reinforced during the mid-1900’s, when Lamarckism was largely rejected while Darwinism was enshrined in what was called the Modern Synthesis of evolutionary biology (Huxley, 1942; Graham, 2016; Bonduriansky and Day, 2018)
Summary
Biologists have long been interested in why organisms appear to be well-suited to the environments in which they find themselves. Ruling out selection on pre-existing variation as the sole cause of changes in phenotypic frequency is critical to demonstrating adaptive multigenerational plasticity. The strains of P. vranovensis used in this study were isolated from a natural environment of C. elegans, suggesting that heritable resistance to this pathogen would be ecologically relevant and increase fitness in the wild.
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